wgsl: hide naga behind feature

Author: Firestar99

crates/rustc_codegen_spirv/Cargo.toml

@@ -29,6 +29,7 @@ use-compiled-tools = ["spirv-tools/use-compiled-tools"]
 # and will likely produce compile errors when built against a different toolchain.
 # Enable this feature to be able to experiment with other versions.
 skip-toolchain-check = []
+naga = ["dep:naga"]
 
 [dependencies]
 # HACK(eddyb) these only exist to unify features across dependency trees,
@@ -60,7 +61,7 @@ itertools = "0.10.5"
 tracing.workspace = true
 tracing-subscriber.workspace = true
 tracing-tree = "0.3.0"
-naga = { version = "25.0.1", features = ["spv-in", "wgsl-out"] }
+naga = { version = "25.0.1", features = ["spv-in", "wgsl-out"], optional = true }
 
 # required for cargo gpu to resolve the needed target specs
 rustc_codegen_spirv-target-specs.workspace = true

crates/rustc_codegen_spirv/src/link.rs

@@ -324,7 +324,7 @@ fn post_link_single_module(
         drop(save_modules_timer);
     }
 
-    if let Some(transpile) = should_transpile(sess) {
+    if let Ok(Some(transpile)) = should_transpile(sess) {
         transpile(sess, cg_args, &spv_binary, out_filename).ok();
     }
 }

crates/rustc_codegen_spirv/src/naga_transpile.rs

@@ -11,15 +11,25 @@ pub type NagaTranspile = fn(
     out_filename: &Path,
 ) -> Result<(), ErrorGuaranteed>;
 
-pub fn should_transpile(sess: &Session) -> Option<NagaTranspile> {
+pub fn should_transpile(sess: &Session) -> Result<Option<NagaTranspile>, ErrorGuaranteed> {
     let target = SpirvTargetEnv::parse_triple(sess.opts.target_triple.tuple())
         .expect("parsing should fail earlier");
-    match target {
-        SpirvTargetEnv::Naga_Wgsl => Some(transpile::wgsl_transpile),
-        _ => None,
-    }
+    let result: Result<Option<NagaTranspile>, ()> = match target {
+        #[cfg(feature = "naga")]
+        SpirvTargetEnv::Naga_Wgsl => Ok(Some(transpile::wgsl_transpile)),
+        #[cfg(not(feature = "naga"))]
+        SpirvTargetEnv::Naga_Wgsl => Err(()),
+        _ => Ok(None),
+    };
+    result.map_err(|_e| {
+        sess.dcx().err(format!(
+            "Target {} requires feature \"naga\" on rustc_codegen_spirv",
+            target.target_triple()
+        ))
+    })
 }
 
+#[cfg(feature = "naga")]
 mod transpile {
     use crate::codegen_cx::CodegenArgs;
     use naga::error::ShaderError;

tests/compiletests/Cargo.toml

@@ -15,7 +15,7 @@ use-compiled-tools = ["rustc_codegen_spirv/use-compiled-tools"]
 
 [dependencies]
 compiletest = { version = "0.11.2", package = "compiletest_rs" }
-rustc_codegen_spirv = { workspace = true }
+rustc_codegen_spirv = { workspace = true, features = ["naga"] }
 rustc_codegen_spirv-target-specs = { workspace = true, features = ["dir_path"] }
 clap = { version = "4", features = ["derive"] }
 itertools = "0.10.5"